The Program for Pandemic Preparedness by Ventilation, P3Venti, leads, collects and distributes scientific research on the influence and potential impact of ventilation on aerogenic pathogen spread, exposure risk and infection control.
P3Venti has an expected duration of three years (August 2022 – July 2025), is coordinated by TNO, and carried out by a consortium of research institutes and partners financed by the Dutch ministry of health (VWS).
For more in-depth information on the program, please refer to the program summary.
The goal of P3Venti is to support the government and (not-for-profit) stakeholders in their policy and decision making by generating scientific, actionable knowledge. Three key areas can be identified in this task:
Symposium P3Venti
Wednesday the 28th of February 2024 the first symposium of P3Venti took place in Zoetermeer.
read moreScience
A critical part of P3Venti is fundamental scientific research. Scientific publications will be collected on a database on this website as they are published.
Our research aims to build knowledge in several key areas:
Research areas
Technical research
This research includes studying exposure risks and the effect of ventilation measures, observations in operational conditions such as elderly care homes, interviews with stakeholders and occupants, computer modeling and experimental particle dispersion and airflow vector research both in a mock-up and in-situ.
What contribution do ventilation and the use of air purifiers etc. make to preventing infection?
Influence of indoor environmental conditions, such as humidity and temperature.
Implementation and policy-making
Knowledge from the other two areas is collected and combined with social-scientific methods to better transfer the knowledge to, and facilitate the implementation of measures for the users.
Prioritization. In which sectors of society is (investing in) ventilation as a prevention measure most needed and most effective?
Proportionality and cost/benefit of application of ventilation.
Biomedical research
Investigation of viability and infectivity of virus-bearing particles (especially related to SARS-CoV-2) in relation to time and size distribution. Focus on literature studies and experimental research.
The contribution of aerogenic transmission to the total transmission of a virus.
The dose-response relationship in air, i.e. how many virus particles are needed to cause infection through aerogenic transmission?
Network
To ensure the accessibility and dissemination of the scientific findings and knowledge, P3Venti is establishing a knowledge network.
The core of the knowledge network are the members of a broad scientific sounding board, and the researchers within the program. From this core, the network will expand and grow as the program matures, facilitating partnerships and collaboration between related scientific programs and projects, such as PDPC, CLAIRE and MIST; as well as promoting collaboration and feedback with healthcare institutions and regulatory bodies.
With this network, P3Venti not only provides answers to the specific research questions defined for this program, but also contributes to the strengthening of the knowledge base needed to identify and effectively address new research questions and needs in a timely manner.
The network will increasingly expand to include delegated professionals connected to long-term care and possibly from other social sectors. As such, P3Venti is actively looking to make national and international connections with interested scientists and organizations to start exchanging knowledge and expertise. In this spirit, we would like to invite and encourage you to reach out and contact us if you have any interest in joining the Network by attending our symposium, joining our LinkedIn group, following the LinkedIn information page, or sending any questions to penvoerder-p3venti@tno.nl.
An initial overview of current key players within the knowledge network can be found on the network page.
Links:
Practice
Based on the knowledge gained and collected through P3Venti, we strive to provide practical measures, methods and guidelines to help healthcare institutions and regulatory bodies to be better prepared for the next pandemic. A vital aspect is to as much as possible ensure healthy and enjoyable living conditions under these measures. Here you can find questions, answers and tips on how ventilation and air purification can contribute to reducing the spread of viruses through the air.
Questions and answers
Effectiveness of ventilation and air purifiers
Can I reduce infection risk through ventilation?
Ventilation can reduce the concentration of aerosols (small airborne particles) – and therefore viruses - in a space. However, the way most buildings are currently ventilated will have little to no effect when the source of the aerosols and the receiver (person) are close to each other. In addition, very large particles (larger than 100 µm) will hardly be influenced by air currents, so their behaviour is more dependent on gravitational effects. Ventilation can contribute in particular to reducing the concentration of mostly smaller particles that travel and spread over longer distances. However, this is subject to the certain important conditions.
As much as possible, try and avoid the recirculation of air throughout multiple spaces (whereby air is extracted from one space to be supplied to another). The application of recirculating units within the same space for (additional) heating and/or cooling is not a problem as long as enough fresh air is supplied (ventilation). Virus particles will spread throughout the space regardless of recirculating units, which through additional mixing only shorten the time needed for these particles to spread. Important to note is that strong air currents greatly increase the distance exhalations (particle clouds/plumes) travel through the air. Through this route, other people in the room could potentially be infected over distances exceeding 1.5m.
The recirculation of air across multiple spaces in a building is a system that is rarely used in the Netherlands and, if so, almost exclusively in older buildings. With a sufficient supply of fresh air, the natural dilution or removal of particles through ventilation is adequate, so this may not be a problem. In buildings with increased amounts of infected individuals and/or ‘corona risk-groups’ (cohorts), these recirculation mechanisms are best not used. In these cases it is better to exclusively use fresh air supply for ventilation to answer to the need of preventing avoidable ‘risks’.
An important aspect for the effectiveness of ventilation systems is ensuring their proper use. If a ventilation system is not used or maintained properly, the intended and potential effect cannot be reached. The website www.ventilerenzogedaan.nl provides several tips for the correct use of ventilation systems.
Several studies have shown that virus particles can travel through the air inside aerosols. For example, in a study by Peng et al., various Covid-19 outbreaks were modelled and compared with known pathogens such as measles and tuberculosis, the aerogenic transmission characteristics of which are well-documented. This suggests that Covid-19 can also be considered aerogenic.1 It has also been found that these virus particles can continue to be infectious at relatively long distances from their source (approximately 2 meters), and can thus potentially lead to infection.2 The question now is whether the use of ventilation can reduce these infections.
By introducing clean outdoor air (ventilation), the concentration of aerosols can be diluted, reducing the risk of infection through airborne particles.3 Several studies accordingly consider ventilation to be an efficient, feasible, and acceptable intervention to reduce the risk of infection through the aerogenic route.4 Determining the effectiveness of ventilation and (pathogenic) particle removal from the space, the so-called 'ventilation effectiveness' or 'contaminant removal efficiency', is an important parameter in this regard.5,6 Furthermore, combining ventilation with other methods (such as masks or air filters) was found in a computational study to be the most effective measure for reducing the risk of infection.7
Ventilation can of course also have negative consequences. In some cases, it can even contribute to the spread of aerosols, for example, by recirculating air between different rooms. Central air conditioning is an example of an air handling system that can cause this.8 Ventilation can also negatively impact the indoor thermal and acoustic comfort.9
However, based on the current state of research, the extent to which ventilation reduces the risk of infection cannot be determined.10–22 For example, in a recent study conducted in 10,000 classrooms in the Italian region of De Marke, the likelihood of infection in a mechanically ventilated room was 74% lower than in a naturally ventilated room.23 However, during this study, the students wore face masks at school, including while they were in the classrooms. By implementing this personal protection measure, the contribution of short-distance transmission was likely limited, while potentially increasing the role of long-distance transmission. In this study, such important confounding factors were not thoroughly controlled for in the analysis, leaving the role of ventilation alone unclear.
What has been demonstrated in several studies is that the effectiveness of ventilation is influenced by various factors:
1. Distance to the source of emissions
The concentration of virus particles is highest near the source, regardless of particle size, particularly in exhaled air.24 However, it is evident that current ventilation solutions have little effect on short-distance transmission (close to the source), as airflows play a less important role at short distances, and have little influence on large particles that have not yet precipitated close to the source.25–27 However, scientific literature does not provide a clear view regarding the size of particle released during respiratory activities such as breathing, talking, singing, sneezing, and coughing. This applies to small particles (< 5 µm), larger particles (> 100 µm) and all particles sizes in between. It does seem that the number of emitted particles is proportional to the sound level produced during the respiratory activity (volume).28 Social distancing is an effective way to reduce the risk of infection.3
2. Relative humidity and temperature
Indoor relative humidity and temperature play a role in the airborne spread of certain particle sizes.4 At lower relative humidities (already below 80%), particles ≤ 40 µm will rapidly decrease in size and weight due to evaporation, after which they can be carried much further by an air current.29 For particles ≥ 80 µm, this effect seems negligible.30 However, there are also indications that virus particles in aerosols of 5-10 µm are deactivated more quickly at lower relative humidity (<45%).31
Temperature differences (between indoor and outdoor) also affect natural ventilation and consequently particle spread, especially in the case of single-sided ventilation (where ventilation facilities are located in only one façade).7 Temperature differences between rooms can also cause air to circulate more easily in open spaces and even enter rooms with closed doors. These differences can be caused by the location of the room in the building, the position of windows relative to the sun (season-dependent), and other conditions, as well as the presence of people.8
Please note that according to an expert panel, controlling the relative humidity and temperature is considered less effective and feasible for reducing the risk of infection.4
3. The distribution of air in the space (mixing)
In addition to the amount of fresh outdoor air, which in theory has a low concentration of virus particles, the distribution and movement of air throughout the space is important. With an uneven distribution of supplied air, certain parts of the space may be well ventilated while others may not. This can result in situations where the ventilation system contributes to a reduction in concentration in one part of the room while having much less of an effect in another part. The properties and type of the ventilation system play an important role in this. For example, a study by Baig et al. demonstrated that if the intake and exhaust of the ventilation system are integrated into the ceiling, the number of aerosols in the space decreases more than if the exhaust is located at the bottom of the wall.32
Air distribution is also influenced by many other factors such as the layout and furnishing of rooms, the placement of ventilation openings, doors and windows, the movement of people, and even less obvious factors like heat pumps.8,32–35
A space can also be subdivided using doors, screens, curtains, or even air curtains so as to control the distribution of air.8,32,36 This is especially true for places with wide access and a direct connection to an infected location.8 For example, a study has shown that closing curtains between beds in hospitals can reduce the flow of air enough to reduce the spread of aerosols between beds.37
4. Flush time
The time needed to lower particle concentration (flush time) is also important. For example, ventilation may be ineffective if a space is in continuous use with a rapid throughput of people, such as in a busy (enclosed) toilet cubicle.38
5. Diminishing returns from ventilation
Computational research has indicated that the difference between no ventilation and some ventilation is most significant. In other words, if there is already adequate ventilation, further increasing it may not contribute much.39,40 However, there is no known specific amount of ventilation that can bring the number of aerogenic infections to an acceptable level. The study by Jia et al. suggests a value of 10 l/s/person is necessary for short and long-distance exposure to create a situation comparable to the outdoors.41 This quantity is somewhat higher than what is generally specified in the current Dutch Building Code (Bouwbesluit) 2012, but research by Bartels et al. has shown that there seems to be no direct reason to adjust these ventilation requirements.39 Beside the discussion of what is 'acceptable', this depends, among other factors, on the infectivity of the pathogen. For instance, the Omicron variant is more contagious than the Delta variant of the SARS-CoV-2 virus.
Beside the effect of ventilation, another important question is to what extent the airborne route over long distances contributes to the occurrence of infections. This, however, is not yet unequivocally answered. The answer to the question 'What is the contribution of airborne transmission of the SARS-CoV-2 virus over long distances compared to short-distance transmission?' goes into more detail on this topic.
Literature
1. Peng Z, Rojas ALP, Kropff E, et al. Practical Indicators for Risk of Airborne Transmission in Shared Indoor Environments and Their Application to COVID-19 Outbreaks. Environ Sci Technol. 2022;56(2):1125-1137. doi:10.1021/acs.est.1c06531
2. Lednicky JA, Lauzardo M, Hugh Fan Z, et al. Viable SARS-CoV-2 in the air of a hospital room with COVID-19 patients. Int J Infect Dis. 2020;(1):1-20. doi:10.1016/j.ijid.2020.09.025
3. Chen W, Qian H, Zhang N, Liu F, Liu L, Li Y. Extended short-range airborne transmission of respiratory infections. J Hazard Mater. 2022;422(June 2021):126837. doi:10.1016/j.jhazmat.2021.126837
4. de Crane D’Heysselaer S, Parisi G, Lisson M, et al. Systematic Review of the Key Factors Influencing the Indoor Airborne Spread of SARS-CoV-2. Pathogens. 2023;12(3):1-27. doi:10.3390/pathogens12030382
5. Mundt E, Mathisen HM, Nielsen P V., Moser A. REVHA Guidebook No 2 - Ventilation Effectiveness.; 2004.
6. NEN. NEN-EN-ISO 14644-3: Cleanrooms and associated controlled environments - Part 3: Test methods. Published online 2019.
7. Villers J, Henriques A, Calarco S, et al. SARS-CoV-2 aerosol transmission in schools: The effectiveness of different interventions. Swiss Med Wkly. 2022;152(21-22):1-17. doi:10.4414/smw.2022.w30178
8. Horne J, Dunne N, Singh N, et al. Building parameters linked with indoor transmission of SARS-CoV-2. Environ Res. 2023;238(P1):117156. doi:10.1016/j.envres.2023.117156
9. de la Hoz-Torres ML, Aguilar AJ, Costa N, Arezes P, Ruiz DP, Martínez-Aires MD. Reopening higher education buildings in post-epidemic COVID-19 scenario: monitoring and assessment of indoor environmental quality after implementing ventilation protocols in Spain and Portugal. Indoor Air. 2022;32(5):282. doi:10.1111/ina.13040
10. Liu YY, Ning Z, Chen Y, et al. Aerodynamic Characteristics and RNA Concentration of SARS-CoV-2 Aerosol in Wuhan Hospitals during COVID-19 Outbreak. bioRxiv. 2020;86(21):2020.03.08.982637. doi:10.1101/2020.03.08.982637
11. Cowling BJ, Ip DKM, Fang VJ, et al. Aerosol transmission is an important mode of influenza A virus spread. Published online 2013:1-12. doi:10.1038/ncomms2922.Aerosol
12. WHO. Modes of transmission of virus causing COVID-19 : implications for IPC precaution recommendations. Sci Br WHO. 2020;(March):10-12. doi:10.1056/NEJMoa2001316.5.
13. Fennelly KP. Particle sizes of infectious aerosols: implications for infection control. Lancet Respir Med. 2020;8(9):914-924. doi:10.1016/S2213-2600(20)30323-4
14. Huang YC, Tu HC, Kuo HY, et al. Outbreak investigation in a COVID-19 designated hospital: The combination of phylogenetic analysis and field epidemiology study suggesting airborne transmission. J Microbiol Immunol Infect. 2023;56(3):547-557. doi:10.1016/j.jmii.2023.01.003
15. Tellier R. Review of aerosol transmission of influenza A virus. Emerg Infect Dis. 2006;12(11):1657-1662. doi:10.3201/eid1211.060426
16. Judson SD, Munster VJ. Nosocomial transmission of emerging viruses via aerosol-generating medical procedures. Viruses. 2019;11(10). doi:10.3390/v11100940
17. Tran K, Cimon K, Severn M, Pessoa-Silva CL, Conly J. Aerosol generating procedures and risk of transmission of acute respiratory infections to healthcare workers: A systematic review. PLoS One. 2012;7(4). doi:10.1371/journal.pone.0035797
18. Li Y, Huang X, Yu ITS, Wong TW, Qian H. Role of air distribution in SARS transmission during the largest nosocomial outbreak in Hong Kong. Indoor Air. 2005;15(2):83-95. doi:10.1111/j.1600-0668.2004.00317.x
19. Grosskopf K, Mousavi E. Bioaerosols in health-care environments. ASHRAE J. 2014;56(8):22-31.
20. Lindsley WG, Blachere FM, Thewlis RE, et al. Measurements of airborne influenza virus in aerosol particles from human coughs. PLoS One. 2010;5(11). doi:10.1371/journal.pone.0015100
21. Kutter JS, Spronken MI, Fraaij PL, Fouchier RA, Herfst S. Transmission routes of respiratory viruses among humans. Curr Opin Virol. 2018;28:142-151. doi:10.1016/j.coviro.2018.01.001
22. Moriyama M, Hugentobler WJ, Iwasaki A. Seasonality of Respiratory Viral Infections. Annu Rev Virol. Published online 2020:1-19. doi:10.1146/annurev-virology-012420-022445
23. Buonanno G, Ricolfi L, Morawska L, Stabile L. Increasing ventilation reduces SARS-CoV-2 airborne transmission in schools: a retrospective cohort study in Italy’s Marche region. Front public Heal. Published online 2022:1-14.
24. Jones NR, Qureshi ZU, Temple RJ, Larwood JPJ, Greenhalgh T. Two metres or one : what is the evidence for physical distancing in past viruses , argue Nicholas R Jones and colleagues. Published online 2020:1-6. doi:10.1136/bmj.m3223
25. Liu L, Li Y, Nielsen P V., Wei J, Jensen RL. Short-range airborne transmission of expiratory droplets between two people. Indoor Air. 2017;27(2):452-462. doi:10.1111/ina.12314
26. Schijven J, Vermeulen LC, Swart A, et al. Exposure assessment for airborne transmission of SARS-CoV-2 via breathing , speaking , coughing and sneezing. Published online 2020.
27. Tellier R, Li Y, Cowling BJ, Tang JW. Recognition of aerosol transmission of infectious agents: A commentary. BMC Infect Dis. 2019;19(1):1-9. doi:10.1186/s12879-019-3707-y
28. Jacobs P, Borsboom W. 2020 R11031 Ventilatie in Gebouwen En de Invloed Op de Verspreiding van COVID-19.; 2020.
29. Liu L, Wei J, Li Y, Ooi A. Evaporation and dispersion of respiratory droplets from coughing. Indoor Air. 2017;27(1):179-190. doi:10.1111/ina.12297
30. Kompatscher K, Traversari R. TNO 2020 R11208 Rev. 1. Literatuurstudie Naar de Afstand Die Deeltjes (>5 Μm) Afleggen Bij Verschillende Respiratoire Activiteiten.; 2020.
31. Oswin HP, Haddrell AE, Otero-Fernandez M, et al. The dynamics of SARS-CoV-2 infectivity with changes in aerosol microenvironment. Proc Natl Acad Sci U S A. 2022;119(27):1-11. doi:10.1073/pnas.2200109119
32. Baig TA, Zhang M, Smith BL, King MD. Environmental Effects on Viable Virus Transport and Resuspension in Ventilation Airflow. Viruses. 2022;14(3). doi:10.3390/v14030616
33. Humphreys H, Vos M, Presterl E, Hell M. Greater attention to flexible hospital designs and ventilated clinical facilities are a pre-requisite for coping with the next airborne pandemic. Clin Microbiol Infect. 2023;29(10):1229-1231. doi:https://doi.org/10.1016/j.cmi.2023.05.014
34. Beaussier M, Vanoli E, Zadegan F, et al. Aerodynamic analysis of hospital ventilation according to seasonal variations. A simulation approach to prevent airborne viral transmission pathway during Covid-19 pandemic. Environ Int. 2022;158(April 2021). doi:10.1016/j.envint.2021.106872
35. Zhen Q, Zhang A, Huang Q, Li J, Du Y, Zhang Q. Overview of the Role of Spatial Factors in Indoor SARSCoV2 Transmission A Space-Based Framework for Assessing the Multi-Route Infection Risk. Int Journal-of-Environmental-Research-and-Public-Health. Published online 2022.
36. Park SY, Yu J, Bae S, et al. Ventilation strategies based on an aerodynamic analysis during a large-scale SARS-CoV-2 outbreak in an acute-care hospital. J Clin Virol. 2023;165(April):105502. doi:10.1016/j.jcv.2023.105502
37. Cadnum JL, Jencson AL, Alhmidi H, Zabarsky TF, Donskey CJ. Airflow Patterns in Double-Occupancy Patient Rooms May Contribute to Roommate-To-Roommate Transmission of Severe Acute Respiratory Syndrome Coronavirus 2. Clin Infect Dis. 2022;75(12):2128-2134. doi:10.1093/cid/ciac334
38. Denpetkul T, Pumkaew M, Sittipunsakda O, Leaungwutiwong P, Mongkolsuk S, Sirikanchana K. Effects of face masks and ventilation on the risk of SARS-CoV-2 respiratory transmission in public toilets: a quantitative microbial risk assessment. J Water Health. 2022;20(2):300-313. doi:10.2166/WH.2022.190
39. Bartels AA. Effect-van-Verschillende-Ventilatiehoeveelheden-Op-Aerogene-Transmissie-van-Sars-Cov-2. Risicoschatting Op Basis van Het AirCoV2-Model.; 2020.
40. Rocha-Melogno L, Crank K, Bergin MH, Gray GC, Bibby K, Deshusses MA. Quantitative risk assessment of COVID-19 aerosol transmission indoors: a mechanistic stochastic web application. Environ Technol. 2023;44(9):1201-1212. doi:10.1080/09593330.2021.1998228
41. Jia W, Wei J, Cheng P, Wang Q, Li Y. Exposure and respiratory infection risk via the short-range airborne route. Build Environ. 2022;219(April):109166. doi:10.1016/j.buildenv.2022.109166
Can air purifiers reduce infection risks?
In laboratory studies air purification methods seem to be effective in reducing virus particle counts. These air purifiers often also reduce the concentration of particles in a space. However, there is a very limited number of studies showing, in practice, the effectiveness of air purifiers in reducing the chance to be infected with respiratory viruses. Based on this knowledge it is not recommended to trust solely on air purification methods to limit aerogenic transmission risks. The ventilation system should be functioning properly before considering supplementing it with air purification methods. The effectiveness of these methods has been minimally studied or demonstrated in operational conditions, especially concerning the inactivation or transmission of viruses like SARS-CoV-2. Current air purification methods, much like ventilation, will have little to no impact on situations where the particle source and recipient are in close proximity.
When implementing air purification, it's important to be aware of potential negative health effects from prolonged exposure to emitted by-products (such as ozone and potentially UVC).
Air purification equipment is often used to reduce indoor particle concentrations. This equipment improves air quality through filtering, and through its potential to remove or deactivate/kill microbiological contaminants (bacteria, viruses, fungi).1,2 The SARS-CoV-2 pandemic has brought attention to virus inactivation and virus particle removal as important topics. As a result, the use of technologies such as UV and ionization for air purification is gaining attention. However, the effectiveness of these technologies varies widely, and there is limited practical, in-situ research.3-5
Many studies are available that examine filtration, UV, or ionization as purification technologies. Filtration studies, mostly focus on filtering certain particle sizes The neutralisation of microorganisms has received little attention, specifically the inactivation of viruses. The vast majority of studies on UV and ionization conclude that more research is needed to determine the mechanisms and effectiveness of air purification technology for specific microbiological contaminants. Scientific studies do not show consensus in findings regarding effectiveness.1,2,5–12 Air purification has also rarely been investigated in practical settings regarding respiratory viruses.11–16 Two such practical studies examining the effect of air purifiers on viral transmission (actual occurrences of infections) found the purification technology to have no effect.11,14 Laboratory studies are being conducted wherein cultured microorganisms are exposed to UV. The extent to which this inactivates or neutralises the microorganism provides information about its sensitivity to UV. Nebulising microorganisms is more accurate when simulating real situations for practical experiments. The effect is measured by monitoring the decrease in the airborne particle count over time. This method can provide information on filtering ability, but not on the inactivation effectiveness of microorganisms. Methods to determine this inactivation effectiveness exist, but were rarely applied in the examined literature. The effects of constant and intermittent particle sources have not been included in these studies. The assumption is often a one-time emission at the start of the experiment, which is a poor approximation of real situations.
Ionization technologies are studied in relation to non-pathogenic particles. Studies on the effectiveness of ionization regarding the inactivation of microbiological contaminants are scarce.12,17–19 The same is true for practical/in-situ studies.20–23 The few available studies do not draw conclusions about the inactivation of microbiological contaminants or the effectiveness of a specific air purifier.
Studies examining prolonged exposure to UV or by-products released during photocatalytic oxidation (PCO) or ionizing technologies are scarce. Publications do indicate that most commercially available air purifiers emit by-products, although these can vary significantly from the manufacturers stated values. In general, it is advisable to test air purifiers thoroughly based on UV and ionization for by-products. In several European countries, this is common practice or even legally required before they can be used in public spaces. There is literature that suggests that high levels of exposure to electrons released during ionization can lead to negative health effects. Therefore, there may be potential implications related to prolonged exposure to these air purification technologies.
So-called far-UVC lamps with a wavelength of 222 nm are said to be as effective in inactivating viruses as the usual 254 nm. They are also said to produce fewer chemical by-products in moderately to well-ventilated spaces.24 For this reason, UV lamps with a wavelength of 222nm are considered to be safe when used with people present.25 However, there is still insufficient research on the health effects of direct exposure to far-UVC, so the RIVM currently counsels against its use.26 Further research on the release and (prolonged) exposure to (far-)UVC, ozone, released radicals, and ionizing particles on human health is advised.13,27–34
Based on the available literature as well as the varying quality of these studies, no unequivocal conclusions can be drawn regarding the effectiveness of the investigated air purification technologies.4 Therefore, it is recommended to prioritize having adequate ventilation.
1. Liu DT, Phillips KM, Speth MM, Besser G, Mueller CA, Sedaghat AR. Portable HEPA Purifiers to Eliminate Airborne SARS-CoV-2: A Systematic Review. Otolaryngol - Head Neck Surg (United States). 2022;166(4):615-622. doi:10.1177/01945998211022636
2. Mahmoudi A, Tavakoly Sany SB, Ahari Salmasi M, et al. Application of nanotechnology in air purifiers as a viable approach to protect against Corona virus. IET Nanobiotechnology. 2023;(March):289-301. doi:10.1049/nbt2.12132
3. Vermeulen L, Bartels A. Meerwaarde van mobiele luchtreinigers in verminderen van transmissie van SARS-CoV-2 – een literatuurstudie. Published online September 2022. doi:10.21945/RIVM-2022-0134
4. Kompatscher K, Traversari R. Literatuurstudie Naar de Toepassing van Verschillende Luchtreinigingsmethoden Voor Inactivatie van Microbiologische Verontreinigingen.; 2022.
5. Cadnum JL, Jencson AL, Alhmidi H, Zabarsky TF, Donskey CJ. Airflow Patterns in Double-Occupancy Patient Rooms May Contribute to Roommate-To-Roommate Transmission of Severe Acute Respiratory Syndrome Coronavirus 2. Clin Infect Dis. 2022;75(12):2128-2134. doi:10.1093/cid/ciac334
6. Bedell K, Buchaklian A, Perlman S. Efficacy of an automated multi-emitter whole room UV-C disinfection system against Coronaviruses MHV and MERS-CoV. Infect Control Hosp Epidemiol. 2017;37(5):598-599. doi:doi:10.1017/ice.2015.348
7. Green CF, Scarpino P V. The use of ultraviolet germicidal irradiation (UVGI) in disinfection of airborne bacteria. Environ Eng Policy. 2001;3(1):101-107. doi:10.1007/s100220100046
8. Jelden KC, Gibbs SG, Smith PW, et al. Ultraviolet (UV)-reflective paint with ultraviolet germicidal irradiation (UVGI) improves decontamination of nosocomial bacteria on hospital room surfaces. J Occup Environ Hyg. 2017;14(6):456-460. doi:10.1080/15459624.2017.1296231
9. Ko G, First MW, Burge HA. The characterization of upper-room ultraviolet germicidal irradiation in inactivating airbone microorganisms. Environ Health Perspect. 2002;110(1):95-101. doi:10.1289/ehp.0211095
10. Lin WE, Mubareka S, Guo Q, Steinhoff A, Scott JA, Savory E. Pulsed ultraviolet light decontamination of virus-laden airstreams. Aerosol Sci Technol. 2017;51(5):554-563. doi:10.1080/02786826.2017.1280128
11. Welch D, Buonanno M, Grilj V, et al. Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases. Sci Rep. 2018;8(1):1-7. doi:10.1038/s41598-018-21058-w
12. Banholzer N, Zürcher K, Jent P, et al. SARS-CoV-2 transmission with and without mask wearing or air cleaners in schools in Switzerland: A modeling study of epidemiological, environmental, and molecular data. PLoS Med. 2023;20(5):e1004226. doi:10.1371/journal.pmed.1004226
13. Thornton GM, Fleck BA, Dandnayak D, Kroeker E, Zhong L, Hartling L. The impact of heating, ventilation and air conditioning (HVAC) design features on the transmission of viruses, including the 2019 novel coronavirus (COVID-19): A systematic review of humidity. PLoS One. 2022;17(10 October):1-23. doi:10.1371/journal.pone.0275654
14. Menzies D, Popa J, Hanley JA, Rand T, Milton DK. Effect of ultraviolet germicidal lights installed in office ventilation systems on workers’ health and wellbeing: Double-blind multiple crossover trial. Lancet. 2003;362(9398):1785-1791. doi:10.1016/S0140-6736(03)14897-0
15. Su C, Lau J, Gibbs SG. Student absenteeism and the comparisons of two sampling procedures for culturable bioaerosol measurement in classrooms with and without upper room ultraviolet germicidal irradiation devices. Indoor Built Environ. 2016;25(3):551-562. doi:10.1177/1420326X14562257
16. Hofbauer WK, Baßler M. Efficiency of UVC radiation as an air disinfectant in a real environment. In: Indoor Air. ; 2022.
17. Lindblad M, Tano E, Lindahl C, Huss F. Ultraviolet-C decontamination of a hospital room: Amount of UV light needed. Burns. 2020;46(4):842-849. doi:10.1016/j.burns.2019.10.004
18. Hagbom M, Nordgren J, Nybom R, Hedlund KO, Wigzell H, Svensson L. Ionizing air affects influenza virus infectivity and prevents airborne-transmission. Sci Rep. 2015;5:1-10. doi:10.1038/srep11431
19. Hyun J, Lee SG, Hwang J. Application of corona discharge-generated air ions for filtration of aerosolized virus and inactivation of filtered virus. J Aerosol Sci. 2017;107(August 2016):31-40. doi:10.1016/j.jaerosci.2017.02.004
20. Xu Y, Zheng C, Liu Z, Yan K. Electrostatic precipitation of airborne bio-aerosols. J Electrostat. 2013;71(3):204-207. doi:10.1016/j.elstat.2012.11.029
21. Bergeron V, Reboux G, Poirot JL, Laudinet N. Decreasing Airborne Contamination Levels in High-Risk Hospital Areas Using a Novel Mobile Air-Treatment Unit. Infect Control Hosp Epidemiol. 2007;28(10):1181-1186. doi:10.1086/520733
22. Meschke S, Smith BD, Yost M, et al. The effect of surface charge, negative and bipolar ionization on the deposition of airborne bacteria. J Appl Microbiol. 2009;106(4):1133-1139. doi:10.1111/j.1365-2672.2008.04078.x
23. Xia T, Lin Z, Lee EM, Melotti K, Rohde M, Clack HL. Field Operations of a Pilot Scale Packed-bed Non-thermal Plasma (NTP) Reactor Installed at a Pig Barn on a Michigan Farm to Inactivate Airborne Viruses. 2019 IEEE Ind Appl Soc Annu Meet IAS 2019. Published online 2019:7-10. doi:10.1109/IAS.2019.8912457
24. Fennelly M, O’Connor DJ, Hellebust S, et al. Effectiveness of a plasma treatment device on microbial air quality in a hospital ward, monitored by culture. J Hosp Infect. 2021;108:109-112. doi:10.1016/J.JHIN.2020.11.006
25. Peng Z, Miller SL, Jimenez JL. Model Evaluation of Secondary Chemistry due to Disinfection of Indoor Air with Germicidal Ultraviolet Lamps. Environ Sci Technol Lett. 2023;10(1):6-13. doi:10.1021/acs.estlett.2c00599
26. Pereira AR, Braga DFO, Vassal M, Gomes IB, Simões M. Ultraviolet C irradiation: A promising approach for the disinfection of public spaces? Sci Total Environ. 2023;879(December 2022). doi:10.1016/j.scitotenv.2023.163007
27. den Outer P, van Dijk A, Siegersma D, Hagens W. 2021-0050/VLH/WH Notitie UVC En Gezondheid.; 2021.
28. Medical Advisory Secretariat. Air Cleaning Technologies: An Evidence-Based Analysis. Vol 5.; 2005.
29. Jiang SY, Ma A, Ramachandran S. Negative air ions and their effects on human health and air quality improvement. Int J Mol Sci. 2018;19(10). doi:10.3390/ijms19102966
30. Cheek E, Guercio V, Shrubsole C, Dimitroulopoulou S. Portable air purification: review of impacts on indoor air quality and health. Sci Total Environ. Published online 2020:142585. doi:10.1016/j.scitotenv.2020.142585
31. Rijksinstituut voor Volksgezondheid en Milieu. Ionisatoren En Gezondheid.; 2010.
32. Blackhall K, Appleton S, Cates CJ. Ionisers for chronic asthma. Cochrane Database Syst Rev. 2012;(9). doi:10.1002/14651858.CD002986.pub2
33. Alexander DD, Bailey WH, Perez V, Mitchell ME, Su S. Air ions and respiratory function outcomes: A comprehensive review. J Negat Results Biomed. 2013;12(1):1. doi:10.1186/1477-5751-12-14
34. Liu S, Huang Q, Wu Y, et al. Metabolic linkages between indoor negative air ions, particulate matter and cardiorespiratory function: A randomized, double-blind crossover study among children. Environ Int. 2020;138(March):105663. doi:10.1016/j.envint.2020.105663
35. World Health Organization. Ultraviolet Radiation As a Hazard in the Workplace. World Heal Organ. Published online 2003.
How is my ventilation system performing?
What volume of air exchange is sufficient?
Within an acceptable level of estimated risk, there is no immediate reason to deviate from the requirements for new construction outlined in the 2012 ‘Bouwbesluit’ (building code). However, it may be worthwhile to consider higher standards depending on the residents' susceptibility to infection. The 2012 Bouwbesluit ventilation requirement for new-build healthcare buildings is a minimum of 6.5 dm3/s per person. For healthcare bed areas, a fresh air supply of at least 12 dm3/s per person is required.
There are no scientific publications describing the effect of supplying a specific volume of air (ventilation) on the number of potential infections transmitted in a space, or the required degree of ventilation to achieve widely accepted infection levels. However, there are various guidelines, including those from the WHO and CDC, which provide recommended volumes of fresh outdoor air.1,2 The WHO guideline recommends 60 dm3/s per person for healthcare settings. This is significantly higher than the new-build requirements in the 2012 Dutch Building Code (Bouwbesluit). The Bouwbesluit 2012 stipulates a requirement of 0.9 dm3/s per m2 of floor area, with a minimum of 7 dm3/s per person for newly built habitable rooms in residential settings. Regarding healthcare, a threshold value of 12 dm3/s per person in bed areas and 6.5 dm3/s per person in other living areas is given.3
The WHO roadmap was developed after an exploratory study of available literature and an assessment of available guidelines on building ventilation. The literature included in the study seems not to contain research specifically focused on the spread of viruses.1 Recently, The Lancet COVID-19 Commission published a report proposing Non-infectious Air Delivery Rates (NADR) to limit the risk of aerogenic respiratory infections. For schools, offices, and vehicles, a range is recommended from good (10 l/s/person) to best (>14 l/s/person).4
1. WHO. Roadmap to Improve and Ensure Good Indoor Ventilation in the Context of COVID-19.; 2021.
2. de Crane D’Heysselaer S, Parisi G, Lisson M, et al. Systematic Review of the Key Factors Influencing the Indoor Airborne Spread of SARS-CoV-2. Pathogens. 2023;12(3):1-27. doi:10.3390/pathogens12030382
3. Bouwbesluit Online.
4. Allen JG. Proposed Non-infectious Air Delivery Rates ( NADR ) for Reducing Exposure to Airborne Respiratory Infectious Diseases Task Force Members. Lancet. 2022;(November):1-33.
Viral transmission
How is SARS-CoV-2 transmitted?
People can be infected via three routes:
Human-to-human at close range by "direct contact"
By short- and long-range transmission via small droplets (aerosols) containing virus particles (the aerogenic route)
By indirect transmission via surfaces
Ventilation and air purification can potentially reduce the risk of infection through aerosols. For reference, see the question: "Can I reduce infections with ventilation?". Current common solutions for ventilation and air purification have little effect on short-range exposure, but these may contribute to reducing the risk for exposure at longer distances. It is currently unclear what proportion of infections occur by which transmission route.
The effect of continuously cleaning surfaces to prevent the risk of SARS-CoV-2 infections seems limited.
Viruses have three potential transmission routes:
1. human-to-human at close range by direct deposition on mucosal surfaces
2. by short- and long-range airborne transmission via inhalation of small or large droplets containing virus particles (Infectious Respiratory Particles - IRP)1, a.ka. the aerogenic route.
3. by indirect transmission via surfaces (from person to a surface to another person)1–4
The short- and long range aerogenic transmission routes are shown in Figure 1.
Figure 1 Transmission of SARS-CoV-2 via the air; Source: Jimenez.3
1. Short range transmission by direct deposition on mucosal surfaces
Transmission of the SARS-CoV-2 virus (and other viruses) primarily occurs at short distances through droplets and aerosols generated by various respiratory functions like breathing, talking, coughing, and sneezing.6–17 The resulting sound levels of these respirations is related to the number of particles generated. The amount of time between infection and droplet generation plays an important role in the quantity of virus particles present in the exhaled aerosols.18 The available literature on the topic consistently finds a higher risk of transmission at short distances.19,20 Well-known guidelines, such as the 1.5-meter directive from institutions like the RIVM, have been designed with this in mind.
2. Aerogenic route
Originally, direct transmission through large droplets was considered the primary route for infection. However, increasingly this perspective is being critically examined and challenged, as aerosols can play an important role in viral transmission at short distances too.21–24 Beside posing a risk at short distances, aerogenic transmission (by aerosol) can also occur over longer distances. Due to their small size, these aerosols can spread through the air and thus throughout a space.25 There is an increasing amount of literature that examines the aerogenic transmission route. Some studies indicate that infections have occurred through the aerogenic route.22,25 However, collecting direct evidence exclusively for the aerogenic route is very challenging. Currently, it is not possible to determine the degree to which specific transmission routes contribute to infections. In other words, it is unknown what fraction of infections occurs via the aerogenic route, both at short and long distances. Conversely, it is also unknown what portion of infections occurs through other routes.2,6,13,15,26–36
3. Indirect transmission via surfaces
The third and final known infection route is indirect transmission of a virus via surfaces and hand contact. Scientific consensus and insights regarding this transmission route are mainly derived from research on other respiratory viruses.
Virus-containing droplets and particles settle on surfaces. The SARS-CoV-2 virus can remain infectious on a surface for several days37–39 after contact with this surface, virus particles can subsequently be transmitted from hands to the mouth, nose or eyes (mucosal surfaces), leading to infection. While the importance of this route is confirmed by the literature, the extent to which it contributes to the occurrence of infections is not known.2,7,31,40–47 The CDC considers the chance of infection with the SARS-CoV-2 virus through this last route to be small.19,20,48,49
The answer to the question 'Does the SARS-CoV-2 virus remain infectious on surfaces, and what factors influence this?' goes into more detail on this topic.
Literature
1. WHO. Modes of transmission of virus causing COVID-19 : implications for IPC precaution recommendations. Sci Br WHO. 2020;(March):10-12. doi:10.1056/NEJMoa2001316.5.
2. RIVM. Richtlijn COVID-19. 23 november.
3. Jimenez JL, Marr LC, Randall K, Ewing ET, Tufekci Z, Greenhalgh T. What Were the Historical Reasons for the Resistance to Recognizing Airborne Transmission during the COVID-19 Pandemic ? SSRN Electron J. 2021;(May):1-18. doi:10.1111/ina.13070
4. Kutter JS, Spronken MI, Fraaij PL, Fouchier RA, Herfst S. Transmission routes of respiratory viruses among humans. Curr Opin Virol. 2018;28:142-151. doi:10.1016/j.coviro.2018.01.001
5. da Silvia GM. An analysis of the transmission modes of COVID-19 in light of the concepts of Indoor Air Quality. :1-12.
6. Gralton J, Tovey ER, Mclaws ML, Rawlinson WD. Respiratory virus RNA is detectable in airborne and droplet particles. J Med Virol. 2013;85(12):2151-2159. doi:10.1002/jmv.23698
7. Asadi S, Wexler AS, Cappa CD, Barreda S, Bouvier NM, Ristenpart WD. Aerosol emission and superemission during human speech increase with voice loudness. Sci Rep. 2019;9(1):1-10. doi:10.1038/s41598-019-38808-z
8. Morawska L, Johnson GR, Ristovski ZD, et al. Size distribution and sites of origin of droplets expelled from the human respiratory tract during expiratory activities. J Aerosol Sci. 2009;40(3):256-269. doi:10.1016/j.jaerosci.2008.11.002
9. Stadnytskyi V, Bax CE, Bax A, Anfinrud P. The airborne lifetime of small speech droplets and their potential importance in SARS-CoV-2 transmission. Proc Natl Acad Sci U S A. 2020;117(22):19-21. doi:10.1073/pnas.2006874117
10. Qian H, Zheng X. Ventilation control for airborne transmission of human exhaled bio-aerosols in buildings. J Thorac Dis. 2018;10(Suppl 19):S2295-S2304. doi:10.21037/jtd.2018.01.24
11. Liu YY, Ning Z, Chen Y, et al. Aerodynamic Characteristics and RNA Concentration of SARS-CoV-2 Aerosol in Wuhan Hospitals during COVID-19 Outbreak. bioRxiv. 2020;86(21):2020.03.08.982637. doi:10.1101/2020.03.08.982637
12. Wei J, Li Y. Airborne spread of infectious agents in the indoor environment. Am J Infect Control. 2016;44(9):S102-S108. doi:10.1016/j.ajic.2016.06.003
13. Cowling BJ, Ip DKM, Fang VJ, et al. Aerosol transmission is an important mode of influenza A virus spread. Published online 2013:1-12. doi:10.1038/ncomms2922.Aerosol
14. Kluytmans van den Bergh MFQ, Buiting AGM, Pas SD, et al. SARS-CoV-2 infection in 86 healthcare workers in two Dutch hospitals in March 2020: a cross-sectional study with short-term follow -up. medRxiv. Published online 2020.
15. Knibbs LD, Morawska L, Bell SC. The risk of airborne influenza transmission in passenger cars. Epidemiol Infect. 2012;140(3):474-478. doi:10.1017/S0950268811000835
16. Linde KJ, Wouters IM, Kluytmans JAJW, et al. Detection of SARS-CoV-2 in Air and on Surfaces in Rooms of Infected Nursing Home Residents. Ann Work Expo Heal. 2022;XX(Xx):1-12. doi:10.1093/annweh/wxac056
17. Randall K, Ewing ET, Marr LC, Jimenez JL, Bourouiba L. How did we get here: what are droplets and aerosols and how far do they go? A historical perspective on the transmission of respiratory infectious diseases. Published online 2021. doi:10.1098/rsfs.2021.0049
18. Peng Z, Rojas ALP, Kropff E, et al. Practical Indicators for Risk of Airborne Transmission in Shared Indoor Environments and Their Application to COVID-19 Outbreaks. Environ Sci Technol. 2022;56(2):1125-1137. doi:10.1021/acs.est.1c06531
19. Tang JW, Bahnfleth WP, Bluyssen PM, et al. Dismantling myths on the airborne transmission of severe acute respiratory syndrome coronavirus (SARS-CoV-2) Narrative. J Hosp Infect. Published online 2021. doi:10.1016/j.jhin.2020.12.022
20. Chen W, Qian H, Zhang N, Liu F, Liu L, Li Y. Extended short-range airborne transmission of respiratory infections. J Hazard Mater. 2022;422(June 2021):126837. doi:10.1016/j.jhazmat.2021.126837
21. RIVM. Aerogene verspreiding SARS-CoV-2 en ventilatiesystemen ( onderbouwing ).
22. Tran K, Cimon K, Severn M, Pessoa-Silva CL, Conly J. Aerosol generating procedures and risk of transmission of acute respiratory infections to healthcare workers: A systematic review. PLoS One. 2012;7(4). doi:10.1371/journal.pone.0035797
23. Li Y, Huang X, Yu ITS, Wong TW, Qian H. Role of air distribution in SARS transmission during the largest nosocomial outbreak in Hong Kong. Indoor Air. 2005;15(2):83-95. doi:10.1111/j.1600-0668.2004.00317.x
24. Grosskopf K, Mousavi E. Bioaerosols in health-care environments. ASHRAE J. 2014;56(8):22-31.
25. Lindsley WG, Blachere FM, Thewlis RE, et al. Measurements of airborne influenza virus in aerosol particles from human coughs. PLoS One. 2010;5(11). doi:10.1371/journal.pone.0015100
26. Chen W, Zhang N, Wei J, Yen HL, Li Y. Short-range airborne route dominates exposure of respiratory infection during close contact. Build Environ. 2020;176(March):106859. doi:10.1016/j.buildenv.2020.106859
27. Moriyama M, Hugentobler WJ, Iwasaki A. Seasonality of Respiratory Viral Infections. Annu Rev Virol. Published online 2020:1-19. doi:10.1146/annurev-virology-012420-022445
28. Shiu EYC, Leung NHL, Cowling BJ. Controversy around airborne versus droplet transmission of respiratory viruses: Implication for infection prevention. Curr Opin Infect Dis. Published online 2019. doi:10.1097/QCO.0000000000000563
29. Buonanno G, Stabile L, Morawska L. Estimation of airborne viral emission: quanta emission rate of SARS-CoV-2 for infection risk assessment. medRxiv. Published online 2020:2020.04.12.20062828. doi:10.1101/2020.04.12.20062828
30. Tellier R. Review of aerosol transmission of influenza A virus. Emerg Infect Dis. 2006;12(11):1657-1662. doi:10.3201/eid1211.060426
31. Judson SD, Munster VJ. Nosocomial transmission of emerging viruses via aerosol-generating medical procedures. Viruses. 2019;11(10). doi:10.3390/v11100940
32. Doremalen N van, Bushmaker T, Morris DH, Holbrook MG, Gamble A, Williamson BN. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. N Engl J Med. Published online 2020:1-3. doi:10.1056/NEJMc2004973
33. Kampf G, Todt D, Pfaender S, Steinmann E. Persistence of coronaviruses on inanimate surfaces and their inactivation with biocidal agents. J Hosp Infect. 2020;104(3):246-251. doi:10.1016/j.jhin.2020.01.022
34. Chin A, Chu J, Perera M, et al. Stability of SARS-CoV-2 in different environmental conditions. Lancet Infect Dis. 2020;5247(20):2020.03.15.20036673. doi:10.1016/S2666-5247(20)30003-3
35. Sandora TJ, Shih MC, Goldmann DA. Reducing absenteeism from gastrointestinal and respiratory illness in elementary school students: A randomized, controlled trial of an infection-control intervention. Pediatrics. 2008;121(6). doi:10.1542/peds.2007-2597
36. Otter JA, Donskey C, Yezli S, Douthwaite S, Goldenberg SD, Weber DJ. Transmission of SARS and MERS coronaviruses and influenza virus in healthcare settings: The possible role of dry surface contamination. J Hosp Infect. 2016;92(3):235-250. doi:10.1016/j.jhin.2015.08.027
37. Azor-Martínez E, Gonzalez-Jimenez Y, Seijas-Vazquez ML, et al. The impact of common infections on school absenteeism during an academic year. Am J Infect Control. 2014;42(6):632-637. doi:10.1016/j.ajic.2014.02.017
38. Snyder KM. Does Hand Hygiene Reduce Influenza Transmission? J Infect Dis. 2010;202(7):1146-1147. doi:10.1086/656144
39. Yang C. Does hand hygiene reduce SARS-CoV-2 transmission? Graefe’s Arch Clin Exp Ophthalmol. Published online 2020:5-6. doi:10.1007/s00417-020-04652-5
40. Santarpia JL, Rivera DN, Herrera V, et al. Transmission Potential of SARS-CoV-2 in Viral Shedding Observed at the University of Nebraska Medical Center. medRxiv. Published online 2020:2020.03.23.20039446. doi:10.1101/2020.03.23.20039446
41. Döhla M, Wilbring G, Schulte B, et al. SARS-CoV-2 in environmental samples of quarantined households. medRxiv. Published online June 2020:2020.05.28.20114041. doi:10.1101/2020.05.28.20114041
42. Fischer EP, Fischer MC, Grass D, Henrion I, Warren WS, Westman E. Low-cost measurement of face mask efficacy for filtering expelled droplets during speech. Sci Adv. 2020;6(36). doi:10.1126/sciadv.abd3083
43. Lewis D. COVID-19 rarely spreads through surfaces. So why are we still deep cleaning? Nature. 2021;590(7844):26-28. doi:10.1038/D41586-021-00251-4
44. Science Brief: SARS-CoV-2 and Surface (Fomite) Transmission for Indoor Community Environments | CDC.
45. Kitagawa H, Nomura T, Nazmul T, et al. Effectiveness of 222-nm ultraviolet light on disinfecting SARS-CoV-2 surface contamination. Am J Infect Control. 2020;000:17-19. doi:10.1016/j.ajic.2020.08.022
46. Lindblad M, Tano E, Lindahl C, Huss F. Ultraviolet-C decontamination of a hospital room: Amount of UV light needed. Burns. 2020;46(4):842-849. doi:10.1016/j.burns.2019.10.004
47. Welch D, Buonanno M, Grilj V, et al. Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases. Sci Rep. 2018;8(1):1-7. doi:10.1038/s41598-018-21058-w
48. Kompatscher K, Traversari R. Literatuurstudie Naar de Toepassing van Verschillende Luchtreinigingsmethoden Voor Inactivatie van Microbiologische Verontreinigingen.; 2022.
49. Ratnesar-shumate S, Williams G, Green B, et al. OUP accepted manuscript. J Infect Dis. 2020;(52281):1-9. doi:10.1093/infdis/jiaa274
What is the contribution of airborne transmission of the SARS-CoV-2 virus over long distances compared to short-distance transmission?
Despite the lack of certainty regarding the extent to which long-range infections contribute to overall indoor infection, the following is advised from a precautionary point of view:
Reduce the potential indoor aerogenic contamination risk. This means: limiting the number of pathogenic (infectious) virus particles in the air.
To this end, supplying the room with sufficient fresh air is the most straightforward solution. If there is insufficient ventilation, aerogenic transmission over long distances may become more significant.33 An effective way to ventilate is to make good use of the ventilation system (see also www.ventilerenzogedaan.nl).
Air purification through filtration or UV-C exposure is seen as a potential complement to ventilation for reducing pathogen exposure. Barring specific situations, the application of air cleaning is not a standard solution. As of yet, air purification has not been proven effective in reducing infection rates in practice. However, many air cleaning techniques can be used to reduce the number of airborne particles, with the exception of UV-C.
It is worth noting that proper ventilation is not only important for reducing the risk of virus contamination. The main reason for ventilation is to maintain a healthy and comfortable indoor environment by reducing nuisances caused by for example odors, or exposures to emissions from building materials.
More and more literature is becoming available concerning the infection route through aerogenic transmission.1 Although it has not been unequivocally answered yet, indications have been found in several studies that infections have occurred over longer distances via the aerogenic route (>1,5m). The so-called superspreading events, especially, do suggest the occurrence of long-distance transmission.2,3 However, determining the impact of long-distance compared to shorter-distance transmission is difficult due to insufficient information regarding the circumstances surrounding the infections. In other words, it is unknown what percentage of infections occurs through long or short distance exposure. What is known, is that it is situation-dependent, with the following factors playing a role:
1. The presence and performance of ventilation measures
During respiratory activities such as breathing, talking, coughing, and sneezing, aerosols (particles) and respiratory droplets of various sizes are emitted, which are then carried along with the airflow. By influencing the airflow, ventilation affects the dilution and spread of aerosols.4–18 The answer to the question 'Can I reduce infection risk through ventilation?' goes into more detail on this topic.
2. Rate of evaporation and air current
Evaporation affects the size and weight of airborne particles, which in turn affects the distance particles and droplets can travel. Respiratory particles and droplets begin to evaporate as soon as they are emitted. If evaporation occurs rapidly, a droplet can cover a greater distance. If evaporation is slow, a droplet will precipitate faster, dependent on its starting size and weight. Relative humidity can have a significant effect on the distance larger particles, between 5 and 40 µm at emission in diameter, can travel. Exhaled particles can reduce in size by about 30% of their original size due to evaporation.19 Airflow is also critical for the distances these particles can travel. Smaller particles, in particular, can travel longer distances, given sufficient airflow.10,20–22
3. The influence of ambient temperature, UV radiation, relative humidity, and CO2 concentration on the viral stability of the SARS-CoV-2 virus
Once outside the body, the infectivity of SARS-CoV-2 slowly reduces, with certain factors possibly accelerating this process. It has been demonstrated under laboratory conditions that high temperatures and/or UV-radiation can contribute to faster inactivation of the virus in aerosols and on surfaces.23–26 Relative humidity may also have some influence on viral stability, with extreme values (both high and low) possibly causing less inactivation than moderate values.27,28
CO2 concentration also appears to have an effect.29 The infectivity of the SARS-CoV-2 virus increases with higher acidity (lower pH) of the virus-carrying aerosols or IRPs (Infectious Respiratory Particles)30. High concentrations of CO2 in the air inhibit the evaporation of bicarbonates from the IRPs, maintaining a higher acidity and consequently a higher infectivity of the virus. In other words, the lower the CO2 concentration in the air, the faster inactivation occurs. This effect seems to be even stronger than that observed with changes in relative humidity.29
Findings similar to the above from practice-based field studies are far less clear and unequivocal. Studies examining correlations between indoor air conditions and COVID-19 cases typically align with lab studies in finding that higher temperatures and a relative humidity in the mid-range reduce the transmission risk (by accelerating inactivation).28,31,32 The exact values required are less clear. Other mechanisms may be in play, such as respiratory tract sensitivity under certain conditions.4 Furthermore, while specific temperature and relative humidity values (as yet to be determined) may reduce transmission risk in theory, this risk reduction may not be practically available, if these values are uncomfortable for humans or cannot be achieved in practical settings.
An additional complicating factor is that there is no consensus on the definitions of aerogenic and droplet transmission.28 In the literature, these terms are used differently, and it’s not always clear what exactly is meant by them.
Literature
1. RIVM. Richtlijn COVID-19. 23 november.
2. Miller SL, Nazaroff WW, Jimenez JL, et al. Transmission of SARS-CoV-2 by inhalation of respiratory aerosol in the Skagit Valley Chorale superspreading event. Indoor Air. 2021;31(2):314-323. doi:10.1111/ina.12751
3. Peng Z, Rojas ALP, Kropff E, et al. Practical Indicators for Risk of Airborne Transmission in Shared Indoor Environments and Their Application to COVID-19 Outbreaks. Environ Sci Technol. 2022;56(2):1125-1137. doi:10.1021/acs.est.1c06531
4. Kutter JS, Spronken MI, Fraaij PL, Fouchier RA, Herfst S. Transmission routes of respiratory viruses among humans. Curr Opin Virol. 2018;28:142-151. doi:10.1016/j.coviro.2018.01.001
5. Liu YY, Ning Z, Chen Y, et al. Aerodynamic Characteristics and RNA Concentration of SARS-CoV-2 Aerosol in Wuhan Hospitals during COVID-19 Outbreak. bioRxiv. 2020;86(21):2020.03.08.982637. doi:10.1101/2020.03.08.982637
6. Tran K, Cimon K, Severn M, Pessoa-Silva CL, Conly J. Aerosol generating procedures and risk of transmission of acute respiratory infections to healthcare workers: A systematic review. PLoS One. 2012;7(4). doi:10.1371/journal.pone.0035797
7. Li Y, Huang X, Yu ITS, Wong TW, Qian H. Role of air distribution in SARS transmission during the largest nosocomial outbreak in Hong Kong. Indoor Air. 2005;15(2):83-95. doi:10.1111/j.1600-0668.2004.00317.x
8. Grosskopf K, Mousavi E. Bioaerosols in health-care environments. ASHRAE J. 2014;56(8):22-31.
9. Lindsley WG, Blachere FM, Thewlis RE, et al. Measurements of airborne influenza virus in aerosol particles from human coughs. PLoS One. 2010;5(11). doi:10.1371/journal.pone.0015100
10. Duval D, Palmer JC, Tudge I, et al. Long distance airborne transmission of SARS-CoV-2: rapid systematic review. BMJ. Published online 2022:1-14. doi:10.1136/bmj-2021-068743
11. Cowling BJ, Ip DKM, Fang VJ, et al. Aerosol transmission is an important mode of influenza A virus spread. Published online 2013:1-12. doi:10.1038/ncomms2922.Aerosol
12. Chen W, Zhang N, Wei J, Yen HL, Li Y. Short-range airborne route dominates exposure of respiratory infection during close contact. Build Environ. 2020;176(March):106859. doi:10.1016/j.buildenv.2020.106859
13. Moriyama M, Hugentobler WJ, Iwasaki A. Seasonality of Respiratory Viral Infections. Annu Rev Virol. Published online 2020:1-19. doi:10.1146/annurev-virology-012420-022445
14. WHO. Modes of transmission of virus causing COVID-19 : implications for IPC precaution recommendations. Sci Br WHO. 2020;(March):10-12. doi:10.1056/NEJMoa2001316.5.
15. Shiu EYC, Leung NHL, Cowling BJ. Controversy around airborne versus droplet transmission of respiratory viruses: Implication for infection prevention. Curr Opin Infect Dis. Published online 2019. doi:10.1097/QCO.0000000000000563
16. Buonanno G, Stabile L, Morawska L. Estimation of airborne viral emission: quanta emission rate of SARS-CoV-2 for infection risk assessment. medRxiv. Published online 2020:2020.04.12.20062828. doi:10.1101/2020.04.12.20062828
17. Tellier R. Review of aerosol transmission of influenza A virus. Emerg Infect Dis. 2006;12(11):1657-1662. doi:10.3201/eid1211.060426
18. Judson SD, Munster VJ. Nosocomial transmission of emerging viruses via aerosol-generating medical procedures. Viruses. 2019;11(10). doi:10.3390/v11100940
19. Mikhailov E, Vlasenko S, Niessner R, Pöschl U. Interaction of aerosol particles composed of protein and salts with water vapor: hygroscopic growth and microstructural rearrangement. Atmos Chem Phys Discuss. 2003;3(5):4755-4832. doi:10.5194/acpd-3-4755-2003
20. Liu L, Li Y, Nielsen P V., Wei J, Jensen RL. Short-range airborne transmission of expiratory droplets between two people. Indoor Air. 2017;27(2):452-462. doi:10.1111/ina.12314
21. Schijven J, Vermeulen LC, Swart A, et al. Exposure assessment for airborne transmission of SARS-CoV-2 via breathing , speaking , coughing and sneezing. Published online 2020.
22. Tellier R, Li Y, Cowling BJ, Tang JW. Recognition of aerosol transmission of infectious agents: A commentary. BMC Infect Dis. 2019;19(1):1-9. doi:10.1186/s12879-019-3707-y
23. Schuit M, Ratnesar-Shumate S, Yolitz J, et al. Airborne SARS-CoV-2 is rapidly inactivated by simulated sunlight. J Infect Dis. 2020;222(4):564-571. doi:10.1093/infdis/jiaa334
24. Dabisch P, Schuit M, Herzog A, et al. The influence of temperature, humidity, and simulated sunlight on the infectivity of SARS-CoV-2 in aerosols. Aerosol Sci Technol. 2021;55(2):142-153. doi:10.1080/02786826.2020.1829536
25. Doremalen N van, Bushmaker T, Morris DH, Holbrook MG, Gamble A, Williamson BN. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. N Engl J Med. Published online 2020:1-3. doi:10.1056/NEJMc2004973
26. Fears AC, Klimstra WB, Duprex P, et al. Comparative dynamic aerosol efficiencies of three emergent coronaviruses and the unusual persistence of SARS-CoV-2 in aerosol suspensions. medRxiv. 2020;2:2020.04.13.20063784. doi:10.1101/2020.04.13.20063784
27. Oswin HP, Haddrell AE, Otero-Fernandez M, et al. The dynamics of SARS-CoV-2 infectivity with changes in aerosol microenvironment. Proc Natl Acad Sci U S A. 2022;119(27):1-11. doi:10.1073/pnas.2200109119
28. de Crane D’Heysselaer S, Parisi G, Lisson M, et al. Systematic Review of the Key Factors Influencing the Indoor Airborne Spread of SARS-CoV-2. Pathogens. 2023;12(3):1-27. doi:10.3390/pathogens12030382
29. Haddrell A, Oswin H, Otero-fernandez M, et al. Ambient Carbon Dioxide Concentration Correlates with SARS-CoV-2 Aerostability and Infection Risk. Preprint. Published online 2023:1-22.
30. WHO. Global Technical Consultation Report on Proposed Terminology for Pathogens That Transmit through the Air.; 2024.
31. Verheyen CA, Bourouiba L. Associations between indoor relative humidity and global COVID-19 outcomes. J R Soc Interface. 2022;19(196). doi:10.1098/rsif.2021.0865
32. Horne J, Dunne N, Singh N, et al. Building parameters linked with indoor transmission of SARS-CoV-2. Environ Res. 2023;238(P1):117156. doi:10.1016/j.envres.2023.117156
33. Chen W, Qian H, Zhang N, Liu F, Liu L, Li Y. Extended short-range airborne transmission of respiratory infections. J Hazard Mater. 2022;422(June 2021):126837. doi:10.1016/j.jhazmat.2021.126837
Do many SARS-CoV-2 infections occur in the healthcare sector?
The hospital and longterm care systems are at an increased risk regarding respiratory viruses. An important reason is that due to old age, disability or sickness, hospital patients, and care home residents and clients are more likely to have an impaired immune system or comorbidities. As a result, a respiratory disease is more likely to spread and have serious consequences. Gilbert et al. has shown that while only 7% of people infected with COVID-19 in Australia live in care homes, this group accounted for 75% of Australian COVID-19 related deaths.1
This risk of infection is further increased in healthcare settings as groups of people live or reside in close proximity to one another. This applies even more to care homes than to hospitals, as is shown in a Japanese study.2 Another study has shown that in healthcare settings, infections are more often clustered in groups of 5 or more compared to other settings including household, restaurant, and office. In this study, such ‘clusters’ refer to a group of infected people (with a positive SARS-C0V-2 test) who had close contact with the same confirmed case(s), if the onset and confirmation of cases were fewer than 14 days apart.3
Staff in care home facilities can play a major role in spreading viruses as they are regularly in close contact with others (residents and other staff members) as part of their daily routine, according to studies from Spain and the US.4,5 During quarantines, patients, clients and residents rarely leave the healthcare facility’s premises, so there is a small chance for them to be infected elsewhere. Members of staff on the other hand, are often also active outside the facility, and are therefore more likely to introduce a pathogen into the healthcare facility. This risk is heightened for members of staff working at multiple facilities.6 As of yet, it is unknown whether members of staff are infected mostly within or outside of healthcare settings. This seems to be strongly case dependent. 6–8
1. Gilbert GL. Aged care residents — and everybody else — would benefit from better control of COVID-19 transmission. Med J Aust. 2023;218(4):166-167. doi:10.5694/mja2.51843
2. Ueda M, Hayashi K, Nishiura H. Identifying High-Risk Events for COVID-19 Transmission: Estimating the Risk of Clustering Using Nationwide Data. Viruses. 2023;15(2). doi:10.3390/v15020456
3. Imamura T, Watanabe A, Serizawa Y, et al. Transmission of COVID-19 in Nightlife, Household, and Health Care Settings in Tokyo, Japan, in 2020. JAMA Netw Open. 2023;6(2):E230589. doi:10.1001/jamanetworkopen.2023.0589
4. Adams C, Chamberlain A, Wang Y, et al. The Role of Staff in Transmission of SARS-CoV-2 in Long-term Care Facilities. Epidemiology. 2022;33(5):669-677. doi:10.1097/EDE.0000000000001510
5. Montero-Moraga JM, Buron A, Sala M, et al. Impact and management of COVID-19 among healthcare workers in two acute care hospitals and two associated long-term care centres in Barcelona, Spain. NBER Work Pap. Published online 2013:89. http://www.nber.org/papers/w16019
6. Sullivan SG, Sadewo GRP, Brotherton JM, et al. The spread of coronavirus disease 2019 (COVID-19) via staff work and household networks in residential aged-care services in Victoria, Australia, May-October 2020. Infect Control Hosp Epidemiol. 2023;44(8):1334-1341. doi:10.1017/ice.2022.243
7. Cheng VCC, Wong SC, Tong DWK, et al. Multipronged infection control strategy to achieve zero nosocomial coronavirus disease 2019 (COVID-19) cases among Hong Kong healthcare workers in the first 300 days of the pandemic. Infect Control Hosp Epidemiol. 2022;43(3):334-343. doi:10.1017/ice.2021.119
8. Billock RM, Groenewold MR, Sweeney MH, de Perio MA, Gaughan DM, Luckhaupt SE. Reported exposure trends among healthcare personnel COVID-19 cases, USA, March 2020–March 2021. Am J Infect Control. 2022;50(5):548-554. doi:10.1016/j.ajic.2022.01.007
Does the SARS-CoV-2 virus remain infectious on surfaces, and what factors influence this?
According to lab studies, SARS-CoV-2 can remain infectious for hours to days after being deposited on a surface. It can then become airborne again from this surface (resuspension).1–4 Through hand contact, virus particles can then be transferred to the mouth, nose, or eyes (mucosal surfaces) which can lead to infection. The type of surface on which the virus is present may affect its inactivation and the likelihood of transmission.4,5 Generally, SARS-CoV-2 was found less frequently on porous surfaces such as cotton or paper than on non-porous surfaces like metal. This could mean that the virus inactivates faster on porous surfaces (due to different conditions within the porous surface compared to the air) or that it was simply physically more challenging to take samples from porous surfaces.4
Additionally, high temperature and UV intensity/duration also accelerate the inactivation of the SARS-CoV-2 virus on surfaces.4–6 For example, sunlight can inactivate the virus on outdoor surfaces within 20 minutes.7 In some literature, it has been shown that exposure to UV-C can inactivate the SARS-CoV-2 virus on surfaces.8–11 UV-C light could therefore be used for disinfecting surfaces. However, it should be noted that UV-C is harmful to humans, so such disinfection should only be carried out when no people are present. Furthermore, the effectiveness of this virus inactivation method is also highly dependent on the UV-C exposure dose and duration.
On the other hand, the effect of humidity on the inactivation of the SARS-CoV-2 virus on surfaces, is not as clear-cut.6
By now, the general consensus is that transmission via surfaces likely plays a minor role compared to other transmission routes: short-range direct deposition and the airborne route.12,13 The answer to the question 'What is the contribution of airborne transmission of the SARS-CoV-2 virus over long distances compared to short-distance transmission?' goes into more detail on this topic.
Literature
1. Doremalen N van, Bushmaker T, Morris DH, Holbrook MG, Gamble A, Williamson BN. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. N Engl J Med. Published online 2020:1-3. doi:10.1056/NEJMc2004973
2. Kampf G, Todt D, Pfaender S, Steinmann E. Persistence of coronaviruses on inanimate surfaces and their inactivation with biocidal agents. J Hosp Infect. 2020;104(3):246-251. doi:10.1016/j.jhin.2020.01.022
3. Chin A, Chu J, Perera M, et al. Stability of SARS-CoV-2 in different environmental conditions. Lancet Infect Dis. 2020;5247(20):2020.03.15.20036673. doi:10.1016/S2666-5247(20)30003-3
4. Horne J, Dunne N, Singh N, et al. Building parameters linked with indoor transmission of SARS-CoV-2. Environ Res. 2023;238(P1):117156. doi:10.1016/j.envres.2023.117156
5. Cox J, Christensen B, Burton N, et al. Transmission of SARS-CoV-2 in the Workplace: Key Findings from a Rapid Review of the Literature. Vol 57.; 2024. doi:10.1080/02786826.2023.2166394.Transmission
6. Geng Y, Wang Y. Stability and transmissibility of SARS-CoV-2 in the environment. J Med Virol. 2023;95(1). doi:10.1002/jmv.28103
7. Ratnesar-shumate S, Williams G, Green B, et al. OUP accepted manuscript. J Infect Dis. 2020;(52281):1-9. doi:10.1093/infdis/jiaa274
8. Kitagawa H, Nomura T, Nazmul T, et al. Effectiveness of 222-nm ultraviolet light on disinfecting SARS-CoV-2 surface contamination. Am J Infect Control. 2020;000:17-19. doi:10.1016/j.ajic.2020.08.022
9. Lindblad M, Tano E, Lindahl C, Huss F. Ultraviolet-C decontamination of a hospital room: Amount of UV light needed. Burns. 2020;46(4):842-849. doi:10.1016/j.burns.2019.10.004
10. Welch D, Buonanno M, Grilj V, et al. Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases. Sci Rep. 2018;8(1):1-7. doi:10.1038/s41598-018-21058-w
11. Kompatscher K, Traversari R. Literatuurstudie Naar de Toepassing van Verschillende Luchtreinigingsmethoden Voor Inactivatie van Microbiologische Verontreinigingen.; 2022.
12. Katona P, Kullar R, Zhang K. Bringing Transmission of SARS-CoV-2 to the Surface: Is there a Role for Fomites? Published online 2022:1-76.
13. McNeill VF. Airborne Transmission of SARS-CoV-2: Evidence and Implications for Engineering Controls. Annu Rev Chem Biomol Eng. 2022;13:123-140. doi:10.1146/annurev-chembioeng-092220-111631
What is the effect of environmental conditions on the number of SARS-CoV-2 cases?
Field studies that have examined the effect of outdoor environments on the number of SARS-CoV-2 cases and mortality at the population level mainly focus on weather conditions such as temperature, humidity, precipitation, and wind. The results of these studies are inconclusive and sometimes even seem to draw contradictory conclusions. For example, in some studies, wind is the most significant factor, while in others, wind plays no role, and temperature is the most important. In practice, many more factors influence the number of cases or mortality, such as the geographical environment (e.g., altitude and latitude), demographic characteristics, other environmental features like air quality, and human behaviour under different weather conditions and in different countries. Therefore, these complexities make causal relationships difficult to investigate, and the aforementioned studies only offer possible correlations.1–8
Some studies do examine interaction effects between various environmental factors such as temperature, relative humidity, absolute humidity, and multiple weather elements (where the effect of one element on COVID-19 cases depends on another element), which could further explain the inconclusive and contradictory results.5,9
Literature
1. Aboura S. The influence of climate factors and government interventions on the Covid-19 pandemic: Evidence from 134 countries. Environ Res. 2022;208(January):112484. doi:10.1016/j.envres.2021.112484
2. Al-Khateeb MS, Abdulla FA, Al-Delaimy WK. Long-term spatiotemporal analysis of the climate related impact on the transmission rate of COVID-19. Environ Res. 2023;236(P1):116741. doi:10.1016/j.envres.2023.116741
3. Faruk MO, Rana MS, Jannat SN, Khanam Lisa F, Rahman MS. Impact of environmental factors on COVID-19 transmission: spatial variations in the world. Int J Environ Health Res. 2023;33(9):864-880. doi:10.1080/09603123.2022.2063264
4. Ravelli E, Gonzales Martinez R. Environmental risk factors of airborne viral transmission: Humidity, Influenza and SARS-CoV-2 in the Netherlands. Spat Spatiotemporal Epidemiol. 2022;41:100432. doi:10.1016/j.sste.2021.100432
5. Tateo F, Fiorino S, Peruzzo L, et al. Effects of environmental parameters and their interactions on the spreading of SARS-CoV-2 in North Italy under different social restrictions. A new approach based on multivariate analysis. Environ Res. 2022;210(January):112921. doi:10.1016/j.envres.2022.112921
6. Song Q, Qian G, Mi Y, Zhu J, Cao C. Synergistic influence of air temperature and vaccination on COVID-19 transmission and mortality in 146 countries or regions. Environ Res. 2022;215(P1):114229. doi:10.1016/j.envres.2022.114229
7. Song P, Han H, Feng H, et al. High altitude Relieves transmission risks of COVID-19 through meteorological and environmental factors: Evidence from China. Environ Res. 2022;212(PB):113214. doi:10.1016/j.envres.2022.113214
8. Lednicky JA, Lauzardo M, Hugh Fan Z, et al. Viable SARS-CoV-2 in the air of a hospital room with COVID-19 patients. Int J Infect Dis. 2020;(1):1-20. doi:10.1016/j.ijid.2020.09.025
9. Geng Y, Wang Y. Stability and transmissibility of SARS-CoV-2 in the environment. J Med Virol. 2023;95(1). doi:10.1002/jmv.28103
What can I do to reduce virus transmission?
How can I best use the ventilation system?
For the proper use of a ventilation system, please refer to https://www.ventilerenzogedaan.nl [1]. This website provides 5 basic tips on how best to handle a ventilation system to ensure proper use of the ventilation facilities. Additionally, users can create a so-called ‘ventilatiekaart’ or ventilation guide, which shows information on how to best use the ventilation facilities present in the room. By placing this ventilation guide by the entrance to the room, users can quickly understand the correct use of the facilities. The publication ‘Ventilatie in relatie tot COVID-19 en een goede binnenluchtkwaliteit’ can be used to test the amount of ventilation in more detail [2].
[1] Heumen S van, Weerdt C van der, Jacobs P, Traversari R, Hinkema M. Achtergronddocument Handreiking Ventileren Zo Gedaan. Delft, The Netherlands; 2022.
[2] Binnenklimaattechniek. Ventilatie in Relatie Tot COVID-19 En Een Goede Binnenluchtkwaliteit; 2021.
Leadership:
Contact: penvoerder-p3venti@tno.nl
Ir. Lisette Rueb
Program manager, senior project manager
Specialized in the organization of large, innovative projects with various stakeholders.
Dr. Ing. Roberto Traversari MBA
Secretary soundboard group, Scientific lead P3Venti
Researcher and consultant at TNO (Buildings & Energy Systems) in the field of contamination control, energy/sustainability and the physical environment of the hot floor.
Partners
